Filter for electrical waves using plural resonators having similar dominant responseand different spurious response



.0 ,GE INS DOWN 2mm 9 3 s m R Oct. 25, 1966 H. ALBSMEIER FILTER FOR ELECTRICAL WAVES USING PLURAL RESONATOR SIMILAR DOMINANT RESPONSE AND DIFFERENT SPURIOUS Filed Aug. 2'7, 1962 F r/r 0 (kHz) United States Patent FILTER FOR ELECTRICAL WAVES USING PLURAL RESONATORS HAVING SlMILAR DOMINANT RESPONSE AND DIFFERENT SPURIOUS RE- SPONSE Hans Albsrneier, Munich, Germany, assignor to Siemens & Halske Aktiengesellschaft, Berlin and Munich, Germany, a corporation of Germany Filed Aug. 27, 1962, Ser. No. 219,563 Claims priority, application Germany, Sept. 28, 1961, S 75,989 5 Claims. (Cl. 333-72) The invention disclosed herein is concerned with a filter for electrical waves, comprising serially coupled mechanical resonators and at least one electrostrictive transformation system for the transformation of electrical oscillations into mechanical oscillations and vice versa. The transformation system may also be referred to as transformator.

Mechanical resonators always have numerous inherent frequencies which can be due to longitudinal oscillations, bending oscillations, shearing oscillations or torsional oscillations. Mechanical filters constructed with the aid of such resonators therefore often have in practical use respectively several pass ranges and disturbing attenuation break throughs. In a mechanical filter constructed with the aid of longitudinal mode resonators, difficulties of this kind, which were due to bending oscillations of a resonator, were remedied by securing on the resonators attenuation material for the bending oscillations. It is difficult to provide in this manner constant conditions over long periods of time and such expedient results moreover in the following disadvantage: The material for the attenuation of the bending oscillations cannot be practically provided in a manner that would prevent influencing the longitudinal oscillations of the individual resonators, thus resulting in lowering the quality of the mechanical resonators so far as the longitudinal oscillations are concerned, and in turn reducing the selectivity in the working frequency range.

The object underlying the invention has to do with reducing the influence of the undesired inherent resonances which lie outside the desired working frequency of the individual resonator, the reduction of this influence being effected in a manner which is less disturbing with respect to the oscillations of the desired working frequency, and which is also applicable in cases in which the disturbing oscillations are due to the same oscillation type as the kind of oscillations involved in producing the working frequency.

This object is according to the invention realized, in connection with the initially indicated filter for the electrical waves, comprising mutually coupled mechanical resonators, by constructing the resonators differently, so that the inherent frequency of the individual resonator lies in the working frequency range which is specified for the filter, while the further inherent frequencies of the individual resonators are difl erent.

It is in the construction of resonators as bending oscillators of advantage to diiferently load the individual resonators at least at one end thereof, especially by means of material differing from the resonator material, and to select the dimensions (thickness and/or length) of the individual resonators together with the different loadings, so that the inherent frequency of the individual resonator, which frequency is intended as the working frequency, lies in the specified working frequency range of the corresponding filter.

It is in many cases advantageous, and also sufiicient, to differently construct only the transformation members included in the resonators of the filter.

It is of advantage, in the case of resonators constructed as longitudinal oscillators, to form at least some individual resonators, preferably those provided with a transformation member, so that the ratio of diameter to length thereof is different as compared with the remaining resonators. It is thereby desirable, upon constructing the resonators as longitudinal oscillators and having a plurality of electrostrictive transformation members, to make the ratio between the material of the transformation members and the resonator material different.

Of particular importance is the teaching, according to the invention, wherein the resonators of a mechanical filter consist of steel, especially sheet steel.

The resonator loading can be effected in diverse manner. For example, parts of the resonator can be made of different material. Another possibility which may also be used additionally in given cases, resides in making the resonator of a given material and to change the cross-sectional area thereof at some places, for example, enlarging the cross-section at the ends of the corresponding resonator.

Further features of the invention will appear in the course of the description which is rendered below with reference to the accompanying drawing showing examples thereof.

FIG. 1 shows an electromechanical filter two mechanical resonators 1 and 2;

FIG. 2 shows the pass or conduction characteristic of a filter; and

FIG. 3 shows-an example of a resonator provided with electrostrictive material.

Referring now to FIG. 1, the two mechanical resonators 1 and 2 act as longitudinal mode oscillators, such resonators being mechanically coupled over a coupling bridge 3. The system is secured in a suitable housing (not shown), by means of holding wires 4 which grip the respective resonators along a node line of the longitudinal oscillation, the coupling member 3 likewise extending along such node line. The filter is by means of transformation members operated as a quadrupole. The transformation members are electrostrictive ceramic members which are made in the form of blocks 5, 5' and 6, 6 and fastened to the ends of the respective resonators which are made of steel and jointly correspond to the outline of an H. The respective blocks 5, 5' and 6, 6' are metallized at the ends thereof which face away from the respective resonators, terminal wires 7, 7' and 8, 8' extending from the blocks. The terminal wires are very thin so as to avoid affecting the longitudinal oscillations.

The triggering of the filter is effected, for example, over the terminal wires 7, 7' with respect to the metallic holding wire 4, by supplying the wires 7,7 in phase with respect to the holding wire 4. These transformation members operate in a manner similar to a reactive force drive, since the electrostrictive material 5, 5 contacts and expands in timing with the frequency of the supplied alternating voltage, whereby the first resonator, comprising the parts 5, 2 and 5' is upon coincidence of the triggering frequency with an inherent frequency, triggered to oscillate. The resonator 1, 6, 6 is in similar manner provided with transformation means having the connections 8, 8' and 4 which serve as filter output terminals.

If both resonators were constructed similarly so far as the dimensions and amounts of electrostrictive material are concerned, there would result for the filter, which has a desired pass frequency of about 60 kilocycles, a pass frequency such as shown in FIG. 2 in prominent lines. The frequency f is thereby plotted along the abscissa and the transmission attenuation a is plotted along the ordinate. As will be seen from this graph, there are, in addition to the desired pass range of about 60 kilocycles, further pass comprising ranges between about 170 and 180 kilocycles and also in the vicinity of 290 kilocycles.

The pass characteristics may "be caused to assume the course, likewise indicated in FIG. 2, by the use of a simple expedient, namely, by the provision of resonators 1 and 2 of different length L and L and also by the pro.- vision of electrostrictive material, cooperatively associated with these resonators, having different lengths L and L (see FIG. 1). The previously mentioned disturbing resonances (parts A in the graph) have practically disappeared and are somewhat shifted in frequency, and the resonances (parts B in the graph) are now considerably less active.

The graph represented in FIG. 2 shows measurement results obtained with a filter in which the resonator 1, 6, 6' had a ratio of electristrictive ceramic to steel, of 0.3 while the corresponding ratio was 0.4 in the case of the resonator comprising the parts 2, 5, 5'. The qualities of the two resonators differed negligibly but there was obtained a very considerable reduction of the disturbing attenuation disruptions. The scale along the ordinate represents the transmission attenuation of the two-circuit filter in neper. In the desired pass range there results the characteristic which is also indicated in FIG. 2. As will be seen, only the odd numbered harmonic waves are contained in the characteristic. The even numbered harmonic waves are avoided due to the symmetrical input and output at the individual resonators.

For example, upon considering the first five inherent frequencies of compound longitudinal oscillators of the illustrated kind, with different ratios p of electrostrictive material, to the resonator material proper (e.g., steel), there will be obtained, for a desired fundamental oscillation of, for example, 100 kilocycles, the following table:

It will be seen that the coincidence of disturbing inherent frequencies can be very well reduced in the harmful action thereof, already with slight p differences.

The teaching of the invention, is analogously to the longitudinal mode oscillators, likewise applicable in connection with bending oscillators, torsion oscillators and shearing oscillators.

In the case of bending oscillators, the triggering is appropriately effected by the use of electrostrictive material disposed in the oscillation center. This material can be provided, for example, in the case of a beam-shaped bending oscillator, on one side or on both sides thereof. An example of such a resonator is shown in FIG. 3, comprising resonators 1 and 2 having electrostrictive blocks 5 and 6 disposed thereon.

The differences appearing in a given case at the input side with respect to the capacity can be equalized by appropriate step-down coupling to the coil which forms with the capacitance respectively the input or output of the parallel oscillation circuit. This also applies to other oscillators operating as bending oscillators.

It will be as a rule sufficient, in connection witha pural part filter forming a mechanical unit, to make only the mechanical oscillators which contain the transformation members different in the manner according to the invention. It is however possible to construct differently several or all mechanical resonators by loading relating to the distribution of the inherent resonances thereof.

The teaching according to the invention is also applicable, for example, in cases in which several electromechanical filters which are constructed as dipoles are between a plurality of amplifier stages separately interposed and form together with the amplified stages a selective amplifier. The invention is likewise applicable in connection with a plural part filter, according to FIG. 1, in which is provided only one cooperative transformation system, for example, the system comprising the parts 7, 7 and 4, whereby such filter is used in a circuit in the manner similar to a dipole.

Changes may be made within the scope and spirit of the appended claims which define What is believed to be new and desired to have protected by Letters Patent.

I claim:

1. A filter for electrical waves, comprising a plurality of mechanical resonators coupled with one another, an electrostrictive transformer for the transformation of electrical oscillations to mechanical oscillations, and an electrostrictive transformer for the transformation from mechanical oscillations to electrical oscillations, said resonators being so dimensioned that a frequency of each individual resonator lies in the specified working frequenc range of the filter, while the other inherent frequencies of at least some of the individual resonators are different, at least two of said resonators having zones consisting of different materials, the zones on one resonator having a different design from that of the zones on another resonator, so that the said two resonators, while having desired dominant responses at similar frequencies, have corresponding spurious responses at non-similar frequencies.

2. A filter according to claim 1, wherein for each resonator having said zones, one zone is formed by the resonator material proper and the other zone comprises electrostrictive material forming an electrostrictive transformer.

3. A filter according to claim 2, wherein the zones of one of such resonators have dimensions which differ from corresponding zones of another resonator.

4. A filter according to claim 3, wherein said resonators are constructed as longitudinal oscillators and a zone of electrostrictive material is disposed at least on one end of the individual resonators.

5. A filter according to claim 3, wherein resonators are constructed as bending oscillators and said zones of electrostrictive material are disposed intermediate the ends of the respective resonators.

References Cited by the Examiner UNITED STATES PATENTS 2,443,471 6/1948 Mason -1 333-71 2,695,357 11/1954 Douley 333-72 2,814,785 11/1957 Burns 333-71 2,948,867 8/1960 Matteat 33 372 3,015,789 1/1962 Honda 33371 3,064,213 11/1962 Mason 333-71 3,078,427 2/ 1963 Poschenrieder 3337l HERMAN KARL SAALBACH, Primary Examiner.

C. BARAFF, Assistant Examiner. 

1. A FILTER FOR ELECTRICAL WAVES, COMPRISING A PLURALITY OF MECHANICAL RESONATORS COUPLED WITH ONE ANOTHER, AN ELECTROSTRICTIVE TRANSFORMER FOR THE TRANSFORMATION OF ELECTRICAL OSCILLATIONS TO MECHANICAL OSCILLATIONS, AND AN ELECTROSTRICTIVE TRANSFORMER FOR THE TRANSFORMATION FROM MECHANICAL OSCILLATIONS TO ELECTRICAL OSCILLATIONS, SAID RESONATORS BEING SO DIMENSIONED THAT A FREQUENCY OF EACH INDIVIDUAL RESONATOR LIES IN THE SPECIFIED WORKING FREQUENCY RANGE OF THE FILTER, WHILE THE OTHER INHERENT FREQUENCIES OF AT LEAST SOME OF THE INDIVIDUAL RESONATORS ARE DIFFERENT AT LEAST TWO OF SAID RESONATORS HAVING ZONES CONSISTING OF DIFFERENT MATERIALS, THE ZONES ON ONE RESONATOR HAVING A DIFFERENT DESIGN FROM THAT OF THE ZONES ON ANOTHER RESONATOR, SO THAT THE SAID TWO RESONATORS, WHILE HAVING DESIRED DOMINANT RESPONSES AT SIMILAR FREQUENCIES, HAVE CORRESPONDING SPURIOUS RESPONSES AT NON-SIMILAR FREQUENCIES. 